Apparatus for measuring ph



June 30, 1942. F. c. BRENGMAN s-rm. 2,233,180

APPARATUS rn MEASURING pH Filed June 8, 1938 @0671 0715'. Fred C Energy/72a ma!" 3 115072 5 Parker.

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Patented June 30, 1942 APPARATUS FOR. MEASURING pH Fred C. Brengman, Eimhurst, and Milton E. Parker, n, Creamery Company, of Delaware Ill., assignors to Beatrice Chicago, 111., a corporation Application June 8, 1938, Serial No. 212,430

1 Claim.

The present invention relates to the testing of acidity of liquids where it is necessary to know the hydrogen ion concentration of the liquid with a relatively high degree of accuracy.

It is the purpose of the present invention to provide a method and instrument whereby the hydrogen ion concentration in any liquid may be compared with reference to a definite standard in a simple and accurate manner.

It is a further purpose of the present invention to provide means for checking the hydrogen ion concentration of a liquid which means may be readily applied to the existing tanks in which the liquid is stored and which maybe utilized during the treatment of the liquid to bring its hydrogen ion concentration to the desired pH value.

The features and advantages of the invention will appear more fully, as the description proceeds, reference being had to the accompanying drawing wherein a preferred form of the invention is shown. It is to be understood, however, that the drawing and description are illustrative only and are not to be taken as limiting the invention except insofar as it is limited by the claim.

In the drawing,

Fig. 1 is a view in front elevation, certain parts in section, of the testing instrument embodying the present invention;

Fig. 2 is a sectional view taken through a tank in which the liquid under test is stored, showing the manner in which the instrument is applied to the tank, and;

Fig. 3 is a sectionalview taken substantially on the line 3-3 of Fig. 1.

Referring now to the drawing, the present instrument and method utilizes a well-known characteristic of antimony for the purpose of determining the hydrogen ion concentration of a liquid. It is well-known that if an antimony electrode is inserted in any solution having hydrogen and hydroxyl ions in varying concentrations the reaction tends to set up a certain definite electrical potential on the electrode. In the present case, the instrument utilizes two antimony electrodes 5 and 6 of the same crosssectional area. These electrodes are secured in two tubes l and 8 respectively so that each electrode has one end exposed at the lower end of one of the corresponding tubes. The tubes 1 and 8 must be made of some suitable insulating material which is not readily attacked by the acid or alkaline condition of the liquid to be tested. We have found that these tubes can be made of a synthetic resin compound such as that sold under the trade name of Bakelite. The electrodes 5 and 6 are fixed in the lower ends of the tubes 1 and 8 by a suitable cement such as sealing wax. Each electrode has soldered to it a lead wire a which extends upwardly through its respective tube to the upper end thereof. Suitable sealing material, indicated at i0, seals the upper end of each of the tubes 1 and 8. The tubes 1 and 8 are mounted in a housing H which supports a meter I2. The leads 9 go directly to the meter l2. The tubes 1 and 8 may be secured in the housing by any suitable means such as a set screw 13, shown in Fig. 3. The housing I l desirably is provided with a handle H and a hook. The hook I5 is shaped so as to be used for hanging the instrument upon the side wall iii of a tank l1 containing the liquid to be tested.

The tube 8 is adapted to receive a. small container it which container is filled with a standard solution of known hydrogen ion concentration. A collar is is provided on the tube 8 near the lower end thereof and below the collar l9 the tube 8 is threaded on the exterior as indicated at 20. The container l8 has an interior chamber 2| larger in diameter than the lower end of the tube 8. In addition, the container It has a screw threaded portion 22 adapted to receive the screw threaded portion 20 of the tube, 8. At its lower end the container is is closed by means of a thin sheet 23. The sheet 23 is a semi-permeable membrane which prevents any appreciable mixture of the standard solution in the container l8 with the liquid being tested. The membrane will, if the standard solution is immersed in a liquid to be tested for a sufilcient length of time, allow the standard solution and liquid to mix. However, the accuracy of the test can be maintained by changing the standard solution from time to time. The membrane readily permits the conduction of electricity between the electrodes 5 and 6 through the standard solution and the liquid under test. For this membrane 23 we have found that a thin sheet of cellulose material such as is used for sausage casings is satisfactory. The membrane 23 is held in place by a cap 24 screw threaded on the lower end of the container iii, the cap being provided with an opening 25 to expose the membrane 23.

The method of testing the hydrogen ion concentration of a tank I! of liquid is as follows: The container I8 is filled with a solution having a definite and known pH value. This container is then attached to the tube 8 and the entire instrument is lowered into a tank of the liquid which is to be tested. Since the entire operative part of the instrument, namely the two lower ends of the tubes 1 and 8 with the container l8 and the electrodes and 6, is immersed in the liquid, they quickly assume the same temperature as the liquid beingtested. This elimi- Added accuracy is sometimes obtained by utilining a liquid of the kind that is to be tested and adjusting its pH value to a predetermined point. This liquid is then used in chamber l8 as a standard with which to compare the batches to be tested. In this way, we can avoid possible errors which might arise if the standard solution had different characteristics than the liquid under test.

The meter I2 is a micro-ammeter, although any meter capable of measuring the potential diflerence between the electrodes 5 and 6 could be used. The meter I2 will indicate by the deflection of its needle l2a when there is any current flowing between the electrodes 5 and 6. The extent of deflection will indicate the amount of current flowing through the meter. The exposed electrode 5 will be positive with respect to the electrode 6, if the liquid being treated is more acid than the standard solution. Conversely, if the liquid being tested is more alkaline than the standard solution, the exposed electrode 5 will be negative with respect to the electrode 6. Therefore, if the meter i2 is arranged so that its zero deflection is at the center of its scale as shown, the direction of deflection of the meter needle directly indicates whether the liquid is alkaline or acid with respect to .the standard solution.

If the solution in the tank I! is to be adjusted in reaction and is found to be too acid, for example with respect to the reaction of the standard solution in the container l8, it may be corrected by the addition of asuitable alkali such as sodium hydroxide. The liquid may be stirred while the instrument remains in place and the hydrogen ion concentration. adjusteduntil the pointer l2a of the meter l2 returns to zero, or some other predetermined reading. If the reaction of the liquid is adjusted so that the meter reading is zero, this will indicate that the standard in the container II and the liquid being tested have the same hydrogen ion concentration. If the reaction of the liquid is adjusted so that the meter reading is not zero, this will then indicate the relative acidity or alkalinity of the liquid being tested with respect to the standard 'in the container It. The direct transfer of current from one liquid to the other eliminates possibility of error because of complicated comparison methods.

In the event that the electrodes 5 and 6 become dirty or poisoned" by foreign matter, they can readily be cleaned by simply sanding off, using emery paper or some similar abrasive material, the surface of the electrode and the surrounding insulating tube, leaving a fresh, clean surface having the same cross-sectional area as before.

Having thus described our invention, what weclaim as new Patent is:

A portable testing apparatus for measuring pH of a liquid including in combination a housing, an electric meter mounted in said housing, a pair of spaced insulating tubes extending downwardly from said housing so as to be immersible directly together in the liquid whose pH is to be tested, an antimony electrode mounted in the lower end of each of said tubes, the electrode in one of the tubesbeing immersed in the liquid to be tested, an insulating tubular container at the lower end of the other tube and enclosing the electrode therein, said container containing a standard solution to which the electrode therein is always in liquid contact and having a semi-permeable membrane across its lower end to prevent ready mixing of the standard solution and the liquid being treated when both tubes are immersed in the liquid whose pH is to be tested but instantly permitting a current to directly flow through the liquid to be tested and the standard solution, and electrical conductors leading from said electrodes to said meter, said meter indicating any flow of current between said electrodes whereby the exposed electrode will be positive with respect to the electrode in the container if the liquid is more acid than the standard solution and said exposed electrode will be negative if the liquid being tested is more alkaline than the standard solution.

and desire to secure by Letters FRED C. BRENGMAN. MILTON E. PARKER. 

